1. Field of the Invention
This invention relates to novel devices and methods for freezing drops of liquid reagent In particular, it relates to devices and methods for freezing liquid reagents useful in the analysis of biological samples.
In preparing reagents for convenient and efficient testing of clinical biological samples, it is frequently important to obtain dry chemical blends in uniform, discrete amounts. These reagents must be efficiently and economically prepared in small precisely measured quantities. Reagents comprising organic materials, however, tend to spoil or degrade on storage, thus creating quality control problems. Thus, reagents are typically provided in dried form to increase stability. This is preferably done by freezing and lyophilizing the aqueous solutions comprising the reagents to form reagent spheres.
2. Background Art
U.S. Pat. No. 4,848,084 relates to a method and apparatus for the generation of frozen droplets. Liquid is fed under pressure through a nozzle which provides a continuous stream of liquid which breaks apart to form droplets. The cryogenic liquid in the freezing tank is agitated with agitator 20. U.S. Pat. No. 4,982,577 discloses an apparatus and method for freezing droplets of liquid product. The apparatus uses cryogenic liquid, which flows along a ramp or sluiceway to freeze the droplets. U.S. Pat. No. 4,989,416 discloses an elongate tunnel which is inclined to the horizontal and which can be rotated along its longitudinal axis. Rotation of the tunnel carries the particles out of the liquid nitrogen contained therein. U.S. Pat. No. 4,798,614 relates to a freezing apparatus using a rotary chamber which rotates about a horizontal axis. U.S. Pat. No. 4,760,712 discloses a rotary chilling plate on which articles to be frozen are placed in brine. U.S. Pat. No. 4,920,762 discloses a method and apparatus for producing cryogenic targets using a mold assembly. U.S. Pat. No. 4,870,829 discloses a biological freezing apparatus containing a specimen holder which is lowered into a tank comprising a cryogenic liquid. U.S. Pat. No. 4,595,226 relates to a gas sample collection device which includes a specular carousel having at least one reflective surface for holding a sample deposited thereon.
U.S. Pat. No. 4,256,576 relates to a process for the creation of crystal aggregates in one part of the tank by heat transfer from a fluid disposed in another part of the tank. Both parts are separated from each other by a flexible membrane. U.S. Pat. No. 3,282,064 relates to cryogenic or refrigerant regeneration for use in closed cycle systems. U.S. Pat. No. 2,845,472 relates to an apparatus for cooling a transformer and means for recirculating the liquid coolant during the operation of the apparatus. U.S. Pat. No. 2,835,477 relates to an apparatus and method for controlling temperature in a bath. The temperature of the liquid bath is controlled by means of a temperature control conduit immersed in the bath through which the cooling liquid is circulated. U.S. Pat. No. 2,214,009 relates to an apparatus and method for cooling bottled beverages in which the cooling liquid is recirculated through a recirculation loop.